1. Field of the Invention
The invention relates to a vehicle steering system that turns a steered wheel on the basis of an operation of a steering member.
2. Description of Related Art
In recent years, there is known a vehicle steering system equipped with a so-called steer-by-wire system in which a steering member, such as a steering wheel, and steered wheels are not mechanically coupled to each other, and part of a steering transmission system is formed of an electrical path. Such a vehicle steering system includes a steering mechanism connected to a steering member and a steered mechanism that turns tires with the use of a turning motor for turning steered wheels. The steered mechanism executes drive control over the turning motor on the basis of a steering angle that is detected by a steering angle sensor that detects the steering angle of the steering member.
In the thus configured steer-by-wire system, it is important to take fail-safe measures in the case where there occurs an abnormality in the steering angle sensor. Particularly, at the time of a failure in the steering angle sensor, steering operation is difficult even when the steered mechanism is normal. Therefore, for example, a mechanical link that allows easy steering operation even at the time of a failure in the steering angle sensor as suggested in Japanese Patent Application Publication No. 2004-90784 (JP 2004-90784 A) or multiplexed sensors as suggested in Japanese Patent Application Publication No. 10-278826 (JP 10-278826 A) are provided. However, there is a problem that the number of components increases and the cost increases.